This invention relates to a method for stabilising vegetable and animal oils as well as pigments like astaxanthin and canthaxanthin. It also relates to a feed for salmonids, and a method for optimising the effect of the pigment in feed for salmonids.
For the aquaculture industry it has been an economic problem that farmed fish like salmon and trout do not naturally achieve the same strongly red colour as the wild species. Such farmed fish are palely red, if not large amounts of red pigments are artificially supplied, and therefore not as attractive as the wild fish to the customer.
Today pigments like astaxanthin and cantaxanthin are added to the fish feed to make the fish meat more red.
Commercially available astaxanthin products are very expensive and their biological retention is very low (typically 10-12%). In addition astaxanthin is a rather unstable compound, which of course is a drawback. The low stability of astaxanthin is due to oxidation. Commercial pigment products are formulated in order to avoid or reduce oxidation. One typical formulation for astaxanthin is with gelatine and starch. The formulations used are often, however, not optimal with respect to biological availability of the pigment, and a new formulation, combining a high degree of stability with improved biological availability would be of great economical benefit to the aquaculture industry. A more stable pigment is thus highly desired as this would give possibilities for making a formulation more optimal with regard to biological entrance and consequently possibilities for considerably economic saving.
Another problem for the aquaculture industry is degradation and low quality of the fat components in the feed due to oxidation. When marine fat, which is the main fat source in fish feed, reacts with oxygen, firstly primary oxidation products like peroxides are made. Peroxides from polyunsaturated fat are unstable and easily degraded by transformation to secondary oxidation products.
Secondary oxidation products are a complex group of compounds like aldehydes and ketones. To analyse the amount of secondary oxidation products the anisidine value is measured. The anisidine number is the intensity of a colour that develops during reaction between the chemical anisidine and aldehydes in the fat. The anisidine value is given without denomination.
The level of oxidation is often given as totox-value. Totox-value is two times the peroxide value added with the anisidine value.
For fish feed an oil having a totox-value below 20 should be used to secure optimal growth for the fish. It is today difficult to provide oils having a totox-value below 20. Oils with a totox-value of up to 30 are available. By reducing the oxidation oils not nutritional acceptable could be made available as a source for fat in feed. This would be very much appreciated by the aquaculture industry as the supply of fish oils are limited.
Oxidation of fat is a problem also with regard to fat sources like vegetable oils and animal oils other than marine oils.
It has surprisingly been found that by treating fish oils with urea oxidation has been considerably reduced. Even more surprisingly it was notified that oxidation of astaxanthin kept in a fish oil treated by urea was considerably reduced.
The main object of the invention is to provide a method for stabilising vegetable and animal oils with regard to oxidation.
Another main object of the invention is to provide a method for stabilising pigments like astaxanthin and cantaxanthin, with regard to oxidation.
Further, it is an object of the invention to provide a feed for salmonids being improved with regard to storage stability/degradation and biological effect of the pigment.
Still another object of the invention is to provide a method for optimising the effect of the pigment in feed for salmonids.
These and other objects are obtained by treatment or presence of urea as defined in the accompanying claims 1-14.
A preferred feature by this invention is that the oil is treated with urea and added to the fodder before or after extrusion. The oil is treated either by heating in the presence of urea, or by reacting with an aqueous mixture of urea. Another preferred feature is that urea is added directly to the fodder mixture, either in an aqueous phase or in solid form.